Selective oxidation of leucoanthraquinone with pyridine-n-oxide



United States Patent 3,173,929 SELECTIVE OXIDATION OF LEUCOANTHRA-QUINONE WITH PYRIDINE-N-OXIDE Sidney Kasman, Arlington, Mass, assignorto Polaroid Corporation, Cambridge, Mass, a corporation of Delaware N0Drawing. Filed June 16, 1960, Ser. No. 36,477 Claims. (Cl. 260378) Thepresent invention is concerned with chemical processes and moreparticularly with processes for oxidizing leucoan-thraquinone dyes tothe corresponding anthraquinone dyes.

One object of the invention is to provide processes for oxidizingleucoanthraquinones to anthraquinones.

Another object is to provide processes for selectively oxidizing theleucoanthraquinone nucleus of a leucoanthraquinone compound whichcontains other oxidizable moieties in addition to saidleucoanthraquinone nucleus.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

The invention accordingly comprises the process involving the severalsteps and the relation and order of one or more of such steps withrespect to each of the others which are exemplified in the followingdetailed disclosure, and the scope of the application of which will beindicated in the claims.

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed description.

In the preparation of anthraquinone dyes, the dye is often firstproduced in the leuco form and then oxidized to the anthraquinone or, ifproduced as the anthraquinone, may be purified by reduction followed byoxidation. In the past, the oxidation has been generally carried out bya wide variety of methods, varying from heating in sulfuric acid at hightemperatures, with or without other oxidizing agents present, to therelatively mild method of bubbling air through a solution of theleucoanthraquinone. In certain instances, such aerial oxidations,although considered mild, have been found in some instances to oxidizeother moieties present in the dye in addition to the neuclus. Thepresent invention is concerned with providing processes for selectivelyoxidizing the neucleus.

The objects of the present invention are carried out by using N-oxidesof heterocyclic aromatic nitrogen compounds as the oxidizing agent andespecially by using N- oxides selected from the group consisting ofquinoline-N- oxide and pyridine-N-oxide. Particularly good results havebeen obtained with the pyridine-N-oxide. It has been found that suchN-oxides of heterocyclic aromatic nitrogen compounds will selectivelyoxidize the leucoanthraquinone nucleus without oxidizing otheroxidizable moieties which may be present,

The oxidation processes of the present invention have been foundespecially useful to oxidize leucoanthraquinone dye developers toanthraquinone dye developers. Dye developers may be defined as compoundswhich are both dyes and developers of exposed silver halide emulsions.They may be further defined as being compounds which contain within thesame molecule the chromophoric system of a dye and also a silver halidedeveloping function. A preferred class of anthraquinone dye developersare those which comprise an anthraquinone nucleus which is substitutedby radicals which in turn contain silver halide developer radicals,e.g., hydroquinonyl, catechol, etc., radicals. In a preferred embodimentof such compounds the silver halide developing radical is joined to theanthraquinone nucleus through an alkylamino radical. Anthraquinone dyedevelopers are disclosed in copending United States applications such,for example, as the copending application of Richard S. Corley, SerialNo. 485,342, filed January 31, 1955, now US. Patent No. 2,983,605; thecopending application of Elkan R. Blout and Myron S. Simon, Serial No.680,437, filed August 26, 1957, now US. Patent No. 3,047,386; thecopending application of Elkan R. Blout and Myron S. Simon, Serial No.680,619, filed August 27, 1957, now abandoned; and the copendingapplication of Elkan R. Blout, Marilyn R. Cohler, Milton Green, Myron S.Simon and Robert B. Woodward, Serial No. 824,786, filed July 3, 1959,now abandoned. As examples of such developers mention may be made of:

1,4-bisa-methyl-B-hydroquinonyl-ethylamino) -5,8-

dihydroxyanthraquinone.

l -(a-hydroxymcthyl-propylamino -4-(a-1Tl6thYl-[3-hydroquinonylethylamino -anthraquinone.

1-( a-hydroxymethyl-propylamino -4- a-methyl-;3hydroquinonylethylamino)-5, S-dihydroxyanthraquinone.

l-hy-droxy-4- a-methyl-hydroqui nonylethylamino) anthraquinone.

1,4-bisa-methylhydroquinonylpropylamino anthraquinone.

1,5-bis lhydroquinonylmethyl amino-anthraquipone.

1,4-bis-hydroquinonylrr ethylamino-anthraquinone.

1,4-bislx-methyl-fi-hydroquinonylethylamino -6, 7-dichloroanthraquinone.

1- (somethyl-B-hydroquinonylethylamino) -4- (methyl-,6;

hydroquinonylethylamin o -antl1raquinone.

1-( a-methyl-fi-hydroquinonylethylamino -4- (oz-ethyl -5- hydroquinonylethylamino) -5,8dihydroxyanthraquinone.

1,4-bisa-methyl2,5 '-dihydroxybenzyla.mino

anthraquinone.

1,4-bis- (a-methyl-fl-hydroquinon ylethylamino) -5,8-bisbenzene-sulfonamido-anthraquinone.

1,4-bis-(amethyl-,S-hydroquinonylethylamino) -5-hydroxy8-amino-anthraquinone.

1,4-bis- (a-methyl-,8-hydroquinonylethylamino) -5- hydroxyanthraquinone.

1,4-bis- (B-hydroquinonylethylamino -anthraquinone.

I- [p- B-hydroquinonyl-ethyl) -phenyl amino] anthraquinone.

1-( a-hydroxymethyl-propylamino) -4- 8- 4-methyl-2',5

dihydroxyphenyl -a-methyl-ethy1amino] an thraquinone.

1-ethylamino-4- [a (3 ',4-dihydroxyphenyl -ethylamino] anthraquinone.

1-chloro-4- (fi-hydroquinonylethyl amino -anthraquinone.

l -hydroxy-4- [B- (3 ',4-dihydroxyphenyl) -ethylamino] anthraquinone.

I -chloro-5 fi-hydroquinonylethylamino -anthraquinone.

1,4-his-{B-(3,4'-dihydroxyphenyl)-ethylamino]-5,8-

dihydroxyanthraquinone.

1,8-bis- [5- (3 ',4-dihydroxyphenyl -ethylamino] anthraquinone.

1- [B- 3 ',4'-dihydroxyphenyl -ethylamino] -anthraqu inone.

I-fi-h ydroquinonylethylarnino-anthraquinone.

1,5 bis- [fi- 3 ,4'-dihydroxyphenyl -ethylamino] anthraquinone.

1,5-bis- (,B-hydroquinonylethylamino -anthraquinone.

l, S-bis- B-hydroquinonylethylamino) -anthraquinone.

1,5-bisa-methyl-B-hydroquinonylethylamino anthraquinone.

l-(B-hydroxyethylamino) -4- B-hydroquinonylethylarnino) -anthraquinone.

1,4-bis- B- 3,4'-dihydroxyphenyl ethylamino] anthraquinone.

1- (dhydroxyethylamino -4- a-methyl-fi-hydroquinonyh ethylamino)-5,8-dihydroxyanthraquinone.

1,4-bis- (a-ethyl-fi-hydroquinonylethyl amino anthraquinone.

1-methylamino-4- (,B-hydroquinonylethylamino anthraquinone.

1-fl-hydroxyethylamino-4- ot-methyl-p-hydroquinonylethylamino)-anthraquinone.

1,4-bis- 2,5 -dihydroxyanilino -anthraquinone.

N-rnonobenzoyl-1,4-bis- [d(3',4'-dihydroxyphenyl)ethylamino1-anthraquinone.

N-monobenzoyll ,4-bis- 43- 2',5 -dihydroxyphenylethyl amino]-anthraquinone.

4-[1,5-bis (2",5 "-dihydroxyphenyl -3-pentyl] -amino- 1-hydroxyanthraquinone.

1,4-bis-[ 1',5 '-bis-(2",5"-dihydroxyphenyl)-3- pentylamino]-anthraquinone.

It should be noted that the above-mentioned anthraquinones containradicals such, for example, as orthoand para-dihydroxyphenyl radicalswhich are readily oxidizable and, as is known, are capable of developingsilver halide emulsions. In order to preserve the developing ability ofsuch radicals it is important, when preparing the dye developers fromthe leucoanthraquinones through oxidation or by purifying them byreduction followed by oxidation, that the oxidation be limited to theleucoanthraquinone nucleus and not oxidize these radicals. The oxidizingagents, disclosed herein, bring about such a selective oxidation.

In an especially useful embodiment of this invention an excess ofpyridine-N-oxide is employed. A convenient excess has been found to beabout 10% of the equivalent amount; however, it should be understoodthat larger excesses may be used without interfering with theselectivity.

In carrying out the processes of the present invention, theleucoanthraquinone dye and at least an equivalent amount of the N-oxideof the heterocyclic aromatic nitrogen compound are brought into intimatecontact. In a preferred embodiment the dye is dissolved in a solvent andthe oxide is added thereto. If desired the oxide may be first dissolvedin a suitable solvent such, for example, as pyridine. The reaction maybe speeded up, without endangering the selectivity, by carrying it outat a temperature in excess of room temperature. In a preferredembodiment the reaction is carried out at temperatures between about 40C. to 120 C. and more preferably at between 100 C. and 120 C.

The following nonlimiting examples illustrate the processes within thescope of this invention.

Example 1 2.74 gms. of leuco-1,4,5,S-tetrahydroxyanthraquinone and 2.22gms. of 2-aminobutanol were added to 25 mls. of Z-butoxyethanol andreacted at 140 C. under nitrogen for about 5 hours. 25 mls. of pyridinewere added and the reaction was continued overnight. 1.0 gm. of pyridineN-oxide in mls. of pyridine was added and the reaction was continuedovernight at reflux. A spectro photometric analysis indicated that theleuco material had been completely oxidized. The product wasprecipitated into an excess of dilute hydrochloric acid, filtered,washed and dried. The l,4-bis-[a-hydroxymethyl-propylamino]5,S-dihydroxyanthraquinone produced was purified by crystallization fromZ-methoxyethanol.

The mls. of pyridine were added in the above reaction in order toincrease the solubility of the tetrahydroxyanthraquinone.

Example 2 18 gms. of leuco-1,4,5,8-tetrahydroxyanthraquinone, 44 gms. of2-aminopropylhydroquinone hydrobromide, 15.05 gins. of sodiumbicarbonate and 8.15 gms. of boric acid were added to 16 mls. of waterand 329 mls. of Z-methoxyethanol and reacted at reflux under nitrogenfor about 3 hours. 6.24 gms. of pyridine-N-oxide were then added and theoxidation was allowed to proceed at reflux under nitrogen for about 1hour and fifteen minutes. An additional 0.624 gm. of pyridine-N-oxidewas added and the oxidation was continued for another hour. Aspectrophotometric analysis performed at this time indicated the absenceof the leuco compound. The reaction mixture was cooled to roomtemperature, filtered under nitrogen and precipitated into 1,320 mls. of5 to 10% hydrochloric acid. The resulting precipitate was filtered,washed with water and dried under vacuum at 40 C. It was furtherpurified by precipitation from an excess of ethyl acetate into hexane.

Example 3 24.2 gms. (0.10 mole) of leucoquinizarin, 60.0 gms. (0.226mole) of B-(p-aminophenyl)-ethylhydroquinone hydrochloride, 12.4 gms.(0.20 mole) of boric acid, and 21.0 gms. of sodium bicarbonate wereadded to 250 mls. of Znrethoxyethanol. The mixture was slowly brought toreflux, with stirring and under nitrogen and held there for about 20hours. 0.105 mole of pyridine-N-oxide was added and heating wascontinued for about two hours. A spectrophotometric analysis showed thatthe leuco compound had been substantially completely oxidized.- Themixture was cooled and precipitated into an excess of dilutehydrochloric acid and the resulting precipitate was filtered, washed anddried.

The fact that the dye developer, produced in the above examples, readilydeveloped an exposed silver halide @Il'ltllf sion to produce an imageindicated that the hydroquinonyl radicals were not oxidized.

In the above examples boric acid was used in the initial condensationstep and was present during the pyridine N-oxide oxidation. It has beenfound that boric acid catalyzes the oxidation without interfering withthe selectivity. In a preferred embodiment of this invention theoxidation is carried out in the presence of boric acid; The amount ofboric acid used may be varied to suit particular needs. Generally theuse of about 2 moles per mole of dye has been found to substantiallyspeed up the reaction. I

In an especially useful embodiment of this invention, the oxidation iscarried out under a blanket of an inert gas such, for example, asnitrogen. This blanket of inert gas serves to insure against aerialoxidation. It should be understood, however, that it may or may not beused. depending upon ones particular choice.

The dye developers produced by the processes of this invention may beused in photographic products, processes and compositions such as thosedisclosed in the copending United States application of Howard G.Rogers, Serial No. 748,421, filed July 14, 1958, now US. Patent No.2,983,606.

Since certain changes may be made in the above process without departingfrom the scope of the invention herein involved, it is intended that allmatter contained in the above description shall be interpreted asillustrative and not in a limiting sense.

What is claimed is:

1. A process for selectively oxidizing the leucoanthraquinone nucleus ofa leucoanthraquinone compound containing at least one substituentselected from the class consisting of orthoand para-dihydroxyphenylgroups, said dihydroxyphenyl substituent being joined to theleucoanthraquinone nucleus through an amino group present on saidnucleus, to form the corresponding anthra quinone dye without oxidizingsaid dihydroxyphenyl sub stituent, said process comprising reacting saidleucoanthra quinone compound with at least a molar equivalent amount ofpyridine-N-oxide.

2. A process as defined in claim 1 wherein said dihydroxyphenylsubstituent is a para-dihydroxyphenyl group.

3. A process as defined in claim 1 wherein an amount in excess of themolar equivalent amount of said pyridine- N-oxide is employed.

4. A process as defined in claim 1 wherein the reaction.

is carried out at about 40 C. to C.

5. A process as defined in claim 1 wherein the reaction is carried outin the presence of boric acid.

6. A process as defined in claim 1 wherein the reaction is carried outunder a blanket of inert gas.

7. A process for selectively oxidizing the leucoanthraquinone nucleus ofa leucoanthraquinone compound containing at least one substituentselected from the class consisting of orthoand paradihydroxyphenylgroups, said dihydroxyphenyl substituent being joined to theleucoanthraquinone nucleus through an amino group on said nucleus, toform the corresponding anthraquinone dye without oxidizing saiddihydroxyphenyl substituent, said process comprising reacting saidleucoanthraquinone compound with at least a molar equivalent amount ofpyridine-N-oxide under an inert atmosphere in the presence of boric acidat a temperature between about 40 C. to 120 C.

8. A process as defined in claim 7 wherein said dihy droxyphenylsubstituent is joined to the amino group through an alkylene group.

9. In a process of preparing1,4-bis-(m-methyl-B-hydroquinonyl-ethylamino) 5,8dihydroxyanthraquinone, the step comprising refluxingleuco-l,4-bis-(a-methyl,8-hydroquinonyl-ethylamino) 5,8dihydroxyanthraquinone with at least a molar equivalent amount ofpyridine-N- oxide.

10. In a process of preparing 1,4-bis-[p-(fi-hydroquinonyl-ethyl)-phenylamino] anthraquinone, the step comprising refluxingleuco-l,4-bis-[p-(B-hydroquinonylethyl)-phenylamino] -anthraquinone withat least a molar equivalent amount of pyridine-N-oxide.

References Cited in the file of this patent UNITED STATES PATENTS2,185,709 Ogilvie et a1. Jan. 2, 1940 2,207,045 Wilder July 9, 19402,228,885 Olpin Jan. 14, 1941 FOREIGN PATENTS 492,448 Germany Feb. 28,1930 OTHER REFERENCES Baumgarten et al.: Berichte der. deut. chem. Ges.,vol. 71, pp. 2603-6 (1938).

Ochiai: Chem. Abstracts, vol. 41, p. 5880.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,173,929 March 16, 1965 Sidney Kasman It is hereby certified that err orappears in the above numbered patent requiring correction and that thesaid Letters Patent should read as corrected below.

Column 2, line 22, for "l,5bislhydroquinenylmethylamino anthraquinoneread 1,5bishydroquin0nylmethylaminoanthraquinone column 3, line 8 for"-dihydroxyphenyl" read -dihydroxyphenyl) column 6, line 17, for "Feb.28 1930" read Feb 24, 1930 Signed and sealed this 28th day of September1965.

SEAL) Ittest:

ERNEST W. SWIDER EDWARD J. BRENNER nesting Officer Commissioner ofPatents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,173,929 March 16, 1965 Sidney Kasman It is hereby certified that errent requiring correction and that th corrected below.

Column 2, line 22, for "l,S-bislhydroquinonylmethylaminoanthraquinone"read l,5bis-hydroquinonylmethylamino anthraquinone column 3, line 8, for"dihydroxyphenyl" read -dihydroxyphenyl)- column 6, line 17, for "Feb.28, 1930" read Feb. 24, 1930 or appears in the above numbered pat- 6said Letters Patent should read as Signed and sealed this 28th day ofSeptember 1965.

EAL)

lest:

NEST W. SWIDER EDWARD J.

BRENNER testing Officer Commissioner of Patents

1. A PROCESS FOR SELECTIVELY OXIDIZING THE LEUCOANTHRAQUINONE NUCLEUS OFA LEUCOANTHRAQUINONE COMPOUND CONTAINING AT LEAST ONE SUBSITUENTSELECTED FROM THE CLASS CONSISTING OF ORTHO- AND PARA-DIHYDROXYPHENYLGROUPS, SAID DIHYDROXYPHENYL SUBSTITUENT BEING JOINED TO THELEUCOANTHRAQUINONE NUCLEUS THROUGH AN AMINO GROUP PRESENT ON SAIDNUCLEUS, TO FORM THE CORRESPONDING ANTHRAQUINONE DYE WITHOUT OXIDIZINGSAID DIHYDROXYPHENYL SUBSTITUENT, SAID PROCESS COMPRISING REACTING SAIDLEUCOANTHRAQUINONE COMPOUND WITH AT LEAST A MOLAR EQUIVALENT AMOUNT OFPYRIDINE-N-OXIDE.